Air filter



R- B. DAVIS.

0 April 25, 1950 7 AIR FILTER Filed Dec. 29, 1945 Iilllllllll R E m m MN L R E 0 DV T T H N v R Patented Apr. 25, 195

' UNITED STATES. PATENT OF FICE AIR FILTEH R. Burnett Davis, SeattlmWash.

Application December 29, 1945', Serial No. 638,136

' 4 Claims".

The present invention relates toan air filter for use in air conduits and, more particularly, to a method" and means for mounting a filtering element in a frame and for preventing the bypassage ofair' between the peripheral portions of the unit and the conduit or duct wall with which it maybe associated. The invention also relatesto-scertain novel method and means of mounting an filter pad by impaling it during its framing.

prime object of the invention is to provide a novel and improved method of padding filter units whereby the need for fasteners can be dispen'sed' with.

An important object of the invention is the provision, for receiving and supporting a filter pad, of novel frame means which is easily cut, shaped and padded by the use of simple 'toolsiand' relatively unskilled labor, to the end that the finished product is inexpensive enou h to be discarded at the end of a normalperiod of use; such period being determined by the filter material being no longer capable of satisfactorily remov ing "dirt from an air stream.

Afurth'er object of the invention is to provide, imazfilter unit, novel pad receiving and supporting means which frame the pad and engage and hold it merely by an impalement operation, which can' be accomplished by the most unskilled help.

Another object of the'invention is to provide an airfilter which may be simply and quickly installed in an air conduit, even thougheithersor both the filter and conduit are 'no'taccurately "(ll-- mensioned or shaped and yet such assembly will afford a filtering seal between the two elements as. well :as through the filter itself.

llhe .foregoing objects, and others ancillary thereto, I prefer to accomplish as follows:

sAccording to a preferred embodiment of my invention, I dispose within and peripherally about a trance "a filtering medium. or pad, preferably formed of matted filaments or fibers. The pad mayor may not be treated with an oily or viscous dirt-accumulating material which will cause dirt particles to adhere to thefiltering medium. Specifically, the frame is formed of a toothed "strip oil a'relatively thin material having the teeth unid-ireetional'd-isposed alonga common edge. This framing-material may be of fibrous origin,isuchias paper, fiberboard or thelike, or it may be formed of light weight sheet metal. The teeth on the frame material are in turn notched along their sidesso: that, whensuch material is formed in a rectangular frame with the ends joined, as "by stapling or .the'like, a preformed :pad somewhat may be placed upon the teeth of the frame and merely by being pressed downward in a piercing orimpaling action the pad is framed and rein-- forced and, also, a portion of the pad is disposed outwardly of the frame to form a gasket when the filter'pad is in use. It is another and a more panticular object of this invention to provide a filter pad which will be useful in hot air outlets of a normalhot air heating system as used in the home or the like. The filter units may be formed in shapes such as squares, rectangles or circles, depending upon the type of air conduit'to which it is to be accommodated. Employing the construction that I'have shown, the user of the filter merely inserts the filter unit into the air conduit and, regardless of the inaccuracies or poor dimension'ing of that air conduit and regardless of reasonable variationsin the comparative sizes between the cross section of the conduit and the outside oi the filter, the sameis readily positioned and reasonably secured. Under certain circumstances means are incorporated in the frame of the filter unit to assist in frictionally engaging the unit against the wall of the conduit.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended, claims. The invention itself,.however, both .as to its organization and its method of operation, together with additional objects vandaolvantages thereof, will best be understood from the following descripiton of a specific embodiment when read in connection with the accompanying drawing, in which:

Figure 1 is a detailed perspective view of a typical filter unit, the manner of installation in an air conduitbeing suggested in phantom;

"Figure 2 is a lateral cross section taken line'2-.2 of Figure 1.

Figure 3 is an enlarged perspective view showingtdetails of the framing material of my filter um .l iigure disa perspective view of a circular filter um Figure .5 is an. elevational view of a slightly modified form ofstrip of framing material; and Figure '6 .is a fragmentary plan view of the frame material of Figure 5.

A (filter unit, to overcome the defects 'sug gested hereinbefore, must have at least two totally distinctcharacteristics; it must be capable of beingzsimply and inexpensively madeand marketed; and it must also be capable of conforming to .acrelatively wide range of air conduits,

larger than the outside dimensions of the frame while :providing a :filtering seal that :prevents lay-passage of air between the conduit and the filter unit or its frame.

Accordingly, a preferred embodiment of my invention, referring to Figures 1 and 4 of the drawings, i constituted by a frame onto which has been placed and is supported a filtering pad. The frames are preferably formed of die-cut strip material, a typical example of which may be seen in Figure 3. Such a strip ID has formed along one edge, at least, a series of teeth l2, the edges Id of which are notched. Such notches may be either serrate or dentate or in any suitable form which will engage in the matted filaments of the filter pad and thus securely hold the pad. I have found it most expedient to form the frame material from heavy cardboard or fiberboard but it is also contemplated that relatively thin sheet metal and sheet plastic materials will also be used. By properly arranging the cutting means, such as dies, the teeth can be out all equally spaced apart and of like nature, so that two such frame strips can be cut at the same time from a single strip of blank material.

To provide a frame, a toothed strip i formed to the desired size and shape of an air conduit. Next, the ends of the. strip of material forming the frame are joined by staples or stitching as indicated at I 6. There may also be used a crossbrace or truss arrangement formed by one or two legs l8 and (shown as divergent in Figure 1) which are stapled at their ends to the main frame 22.

A conduit, having a rectangular cross-section,

is indicated by the numeral 24 and usually has an opening 26 at right angles thereto. To place the frame 22 within the opening a person need only to remove the usual grill from the opening and insert the frame downward.

Such an easy insertion or installation is largely due to the manner in which the filter pad 30 is mounted in the frame. Thi is accomplished by merely forming a pad of a filamentary material, such as steel wool or spun glass wool or the like, into the general size and shape of the filter frame to be padded and then by impaling or piercing the same, either by pressing it down upon the teeth i2 of the frame or by pressing the frame and its teeth into the filtering material. It is of course desirable that a portion of the filter pad be disposed outside the frame in order that a gasket 32, as seen in Figure 2, is disposed between the frame 22 and the walls of the conduit 24-.

The pad may be treated with an adhesive material, especially around the edges, to weld together certain of the filaments where they cross or lie together. When the frame teeth of such a pad pierce the fibers a very'se'cure grip can be had, if necessary.

Under certain circumstances it has been found desirable to provide adjustable tabs or other means to insure sufiicient engagement between the filter frame and the conduit in which it may be suspended. This is accomplished by providing tongue 34 which projects from the frame'and is shaped or bent outward a sufficient distance so that it will also press against the wall of the conduit. A similar result may be obtained by deforming or bending a tooth in the manner indicated in dotted lines in Figure 3, which tooth then presses outward against the side wall.

In Figure 4 I have shown a circular filter unit, designated as a whole by the reference numeral 40. The only distinction in this latter form is that it is of a circular shape rather than rectangular.

When the unit is in place as a filter, only a thin edged frame is disposed in the air current so that a minimum of air obstruction is offered by the frame structure.

I have found, by employing my method and means, that a filter unit of very low cost can be made which will accommodate itself to a relatively wide range of air'conduit sizes. ;As an example, a 3" x 12" unit can be placed in'a' conduit,

an inch to 1 larger in either dimension, as well as in a conduit in which the clearance is ;less than A" inch. In the former instance the wool around the edge of the filter is merely flufied out more, and in the latter instance, it is compressed more tightly against the frame. In either case the peripheral gasket fringe insures against air passage through space not occupied by filtering fiber material and thus prevents short circuiting of the air.

In- Figure 5 I have shown a portion of strip;

material 52 which has tines or teeth 53 that have been cut by a printers rule or scoring element of conventional nature. In this instance, it will be noted, the edges of the teeth have a series of aligned straight sections separated by outwardly pointed portions which, when the teeth are embedded in a fibrous pad, tend to securelyrestrain fibers from slipping off the teeth. The

frame material of Figures 5 and 6 also has been cut to form the edge tongue 54 which may be bent away from the plane of the main portion oflthe frame to provide a horn having a sharp point which will tend to suspend the frame in anair duct or conduit. As shown in these views the tongue 54 may be twisted slightly thereby to present a very sharp point for the purpose men-- tio'ned.

With reference to the placing of the pad in position on a toothed frame, I have found that it is difiicult to insert teeth straight into the fiber pads because of the action of the roughened edges. This insertion or impaling is materially enhanced by jigging the frame as theteeth move into the fibers and it is further made simple by either jigging the frame and the pad which is being framed relative a mass of bristles, or by tamping the pad when it is properly positioned relative a frame with a stiff bristled member,- such as a whisk-broom or the like; Of course, combinations of the steps may also be used when desired.= If the pad is being impaled in a hand operation I have found that the frame should be placed upon a table with the teeth upward and the pad lying on their tips and then the operator merely tamps the pad with a fairly stiff whiskbroom caused to travel downward toward the teeth whereupon the pad is quickly impaled and the fibers securely entwined around the teeth and under the protrusions thereon.

It has been found that by an application of an'adhesive emulsion of the pressure sensitive type to the fibers forming the gasket fringe 32, when the filter unit is placed in the duct, a degree of adhesion of certain of the fibers to the inner duct surface is obtained. This facilitates suspension of the filter unit in the upright duct. The same material is useful for welding certain edge fibers together, as described, and to hold the pad to the frame and impaling pins.

Also, in certain installations, the entire pad may be sprayed with a dilute solution of an adhesive of the pressure sensitive type, whereby a fewv fibers at least'are welded together and thus strengthen and make the pad more rigid. In such case the pad to a degree becomes self-supporting, and, on occasion, the frame work may be omitted.

While I have shown and described particular embodiments of my invention, it will occur to those skilled in the art that various changes and modifications may be made without departing from the invention, and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

Having thus described my invention, I claim:

1. An impingement type air filter unit primarily useful in air ducts, comprising: an open thin peripheral frame of sheet material formed to slightly less than the size and shape of the duct into which it is intended to be fitted and having the sheet material aligned parallel with the direction of flow of air through said duct and said frame, one edge of said sheet material having extending in alignment therewith a continuous series of elongated teeth, and a pad of loosely disposed filamentary materials of a size and shape slightly larger than said frame and impaled on said teeth to cover said frame opening and extend outwardly therearound to form a peripheral seal between said frame and a wall of such a duct into which the unit is installed, said unit being of such a weight that said outwardly ex- 80 8 tending portion of the pad serves to maintain said unit positioned in an air, duct.

2. An impingement type air filter unit as set forth in Claim '1 in which the edges of the teeth are notched along the sides to catch in and engage the filamentary material of the pad and aid in maintaining the pad on the frame.

3. An impingement type air filter unit as set forth in Claim 1 in which certain of the fibers of the filamentary pad are secured at points of contact between adjacent fibers.

4. An impingement type air filter unit as set forth in Claim 1 in which certain of said teeth are bent over and prevent said pad from becoming dis-impaled from said frame.

R. BURNETT DAVIS.

REFERENCES CITED The following references are of record in the 

